1. Field of the Invention
The present invention relates to an arteriostenosis inspecting apparatus for inspecting absence or presence of arteriostenosis of a superior-limb artery of a living subject. In the present application, the superior-limb artery is defined as encompassing a subclavian artery.
2. Related Art Statement
Atherosclerosis is a sort of arteriosclerosis and is characterized in that lipid, in particular, cholesterol deposits on the inner wall of artery and accordingly the arterial wall thickens. An artery suffering atherosclerosis has stenosis and its diameter reduces. Thus, atherosclerosis is also called arteriostenosis or arteriosclerosis obliterans.
As a device for inspecting arteriostenosis, there is known an ankle-and-brachium-blood-pressure-index measuring device that inspects the stenosis by utilizing a fact that blood pressure lowers on a downstream side of a stenotic portion of an artery. Japanese Patent No. 3140007 or its corresponding U.S. Pat. No. 6,355,000 discloses an example of the index measuring device. The disclosed device includes two cuffs that are adapted to be worn on an ankle and a brachium of a living subject so as to measure an ankle blood pressure and a brachium blood pressure of the subject, respectively, then calculates an ankle-and-brachium blood-pressure index as a ratio between the ankle blood pressure and the brachium blood pressure, and finally inspects presence or absence of arteriostenosis based on the thus calculated ankle-and-brachium blood-pressure index.
Generally, an ankle-and-brachium blood-pressure index is calculated as a proportion of an ankle systolic blood pressure to a brachium systolic blood pressure. In this case, if the thus calculated ankle-and-brachium blood-pressure index is smaller than 0.9, that is, if the ankle systolic blood pressure is smaller than the product of the brachium systolic blood pressure and 0.9, it can be judged that the subject is suspected of arteriostenosis.
In many cases arteriostenosis occurs to an inferior-limb artery, but in some cases it occurs to a superior-limb artery. For example, it is known that the stenosis occurs to a subclavian artery. However, as described above, ankle-and-brachium blood-pressure index is calculated as the proportion of ankle blood pressure to brachium blood pressure. That is, whether the ankle blood pressure is abnormal is judged by comparing the ankle blood pressure with the brachium blood pressure. Therefore, based on the ankle-and-brachium blood-pressure index, it can be judged whether an artery between the heart and the ankle, in particular, an inferior-limb artery has stenosis. However, it is difficult to judge, based on the ankle-and-brachium blood-pressure index, whether a superior-limb artery has stenosis.
It is therefore an object of the present invention to provide an arteriostenosis inspecting apparatus which can inspect presence or absence of stenosis of a superior-limb artery of a living subject.
The above object has been achieved by the present invention. According to the present invention, there is provided an arteriostenosis inspecting apparatus, comprising a left-superior-limb-blood-pressure measuring device which measures a left-superior-limb blood pressure of a left superior limb of a living subject; a right-superior-limb-blood-pressure measuring device which measures a right-superior-limb blood pressure of a right superior limb of the subject; and a left-and-right-superior-limb-blood-pressure-ratio determining means for determining a left-and-right-superior-limb blood-pressure ratio as a ratio between the left-superior-limb blood pressure measured by the left-superior-limb-blood-pressure measuring device and the right-superior-limb blood pressure measured by the right-superior-limb-blood-pressure measuring device.
If one of left and right superior-limb arteries of the subject has stenosis, then the blood pressure in the one artery lowers. Therefore, a left-and-right-superior-limb blood-pressure ratio determined by the left-and-right-superior-limb-blood-pressure-ratio determining means in the case where neither of the left and right superior-limb arteries has stenosis differs from that determined in the case where either of the two superior-limb arteries has stenosis. Thus, based on the left-and-right-superior-limb blood-pressure ratio determined by the left-and-right-superior-limb-blood-pressure-ratio determining means, a person such as a doctor can diagnose presence or absence of arteriostenosis of a superior-limb artery such as a subclavian artery.
Here, preferably, the left-and-right-superior-limb-blood-pressure-ratio determining means determines the left-and-right-superior-limb blood-pressure ratio by using a lower one of the left-superior-limb blood pressure and the right-superior-limb blood pressure as a numerator of the ratio and using a higher one of the left-superior-limb blood pressure and the right-superior-limb blood pressure as a denominator of the ratio. According to this feature, the presence of arteriostenosis always results in lowering the left-and-right-superior-limb blood-pressure ratio. Thus, when the subject suffers arteriostenosis, the left-and-right-superior-limb blood-pressure ratio changes in the same manner as the ankle-and-brachium blood-pressure index as another index useful in diagnosing arteriostenosis. Therefore, misdiagnoses can be reduced.
Also, preferably, the left-and-right-superior-limb-blood-pressure-ratio determining means determines the left-and-right-superior-limb blood-pressure ratio by using a pre-selected one of the left-superior-limb blood pressure and the right-superior-limb blood pressure as a denominator of the ratio. In this case, the person can judge which one of the left and right superior limbs has arteriostenosis, depending upon whether the left-and-right-superior-limb blood-pressure ratio is greater or smaller than 1.